Thanks, Kwag. It might have a slightly different meaning in the states (where a notary public [which is what we use to sign something as true or as actually from the person signing it]) - I know we were looking for this level of commitment in the Daniel commitment - let me look to see if I can find what Jim has said about it (for the US) - now I will say, I don't know what Spain requires, but we should do that which satisfies our own country rules, IMHO.
In this case, this is what Andreas has asked for. An affidavit, which is a sworn testimonial.
That translates to a sworn statement and signed by a notary public (same term here in Puerto Rico, but not sure about Spain)
I guess it all boils down to the same thing, with the same meaning, but just written differently depending on the country.